1. Technical Field
The present invention relates to a vibration damping arrangement used for an apparatus moving along a cable (wire rope, ropeway, etc.) such as cable cars and gondolas of a type which generally includes a supporting device fixed or running on the cable, a hanger suspended from the supporting device and a passenger car suspended from the hanger.
2. Background Art
A cable car facility which includes a passenger car, a hanger for supporting the passenger car and a supporting device (e.g., a cable gripping unit or a traveling roller unit) for supporting the hanger and fixed or running on a cable is advantageous as compared with other transportation systems since it is economically constructed and is able to move in a steep track.
The cable gripping unit may be able to grasp and release the cable or it may be fixed on the cable permanently. The cable is endless and directly circulated by a separate drive. The drive is generally sprockets or pulleys provided at a lower station and an upper station. The endless cable is engaged over these pulleys. The cable car is moved together with the cable. One group of cable car facilities which employ such a cable gripping unit and the separate drive for moving the cable is generally categorized into a single-cable automatically-circulating type or a single-cable fixed carriage type. In the former type the cable gripping unit grasps and release the cable at predetermined positions, and in the latter case the cable gripping unit always holds the cable during conveyance. In either type, only one cable is used. There is another group of cable car facilities which employ more than one cable. In one type of this category, a traveling roller unit rolls on a stationary cable and a drive cable which is moved along the stationary cable is used to move the cable car. The carriage is suspended from the traveling roller unit. The drive cable pulls the traveling roller unit (and in turn the cable car) from the lower station to the upper station along the stationary cable. Generally two stationary cables are provided: one for conveyance from the lower station to the upper station and another for conveyance from the upper station to the lower station. In this case, one cable car is supported at each end of a U-shaped drive cable so that one cable car is pulled to the upper station along one stationary cable when the other cable car is lowered to the lower station along the other stationary cable. The drive for moving the drive cable is a pulley provided at the upper station. This is generally referred to as a reversible aerial tramway. In another type, a plurality of cable cars are fixed on an endless drive cable and the traveling roller units mounted on the cable cars roll on two stationary cables. The cable cars pulled to the upper station move along one stationary cable and the cable cars lowered to the lower station move along the other stationary cable. The drive for moving the drive cable is pulleys provided at the lower and upper stations.
All of these ropeway facilities use a supporting device (a cable gripping unit or a traveling roller unit) and the present invention pertains to any type of such ropeway facilities.
It can be said that the cable car is a single pendulum having its point of support (or a center of oscillation) at a certain point on the cable or on the cable car supporting device, and a cross wind causes the cable car to roll. Such rolling vibration results in uncomfortableness and uneasiness to people in the cable car and in turn stoppage of operation of the cable car to avoid accidents. Conventional cable car facilities have such problems in safety and cost performance. Recently, the cable cars are used not only for mountain side sightseeing but also for a general transportation system. Accordingly, an arrangement for attenuating vibrations of the cable car is desired strongly.
One of vibration damping apparatuses for the cable car is disclosed in Japanese Patent Application Publication No. 5-87183 entitled "Vibration Damping Apparatus". This vibration damping apparatus employs a gyro installed on the cable car for vibration damping and can logically attenuate the vibrations of the cable car. This vibration damping apparatus, however, requires a power source for a motor of the gyro. Generally, it is very difficult for the cable car to have an external power source. Therefore, the above idea is not practical.
Another consideration is needed for the vibration damping apparatus for the cable car: since various structures are provided along the cable and around boarding/stopping stations (e.g., lower, intermediate and upper stations) to drive the cable car along the cable, the vibration damping apparatus mounted on the cable car should not intervene with these structures. In case of a single-ropeway automatically-circulating cable car system, for example, a number of machines is provided at the stopping stations to accelerate/decelerate the cable car, grab/release the cable and open/close doors of the cable car. Along the cable track, provided are structures for supporting and guiding the cable with an appropriate tension and towers and arms for these structures. As mentioned earlier, an attachment (i.e., the vibration damping apparatus) on the cable car should not contact or excessively approach these accessories. In other words, the vibration damping apparatus may project above and below of a main body of the cable car to a certain extent but it is disadvantageous if it projects front, rear, left or right of the body of the cable car.
Another vibration damping apparatus for the cable car is disclosed in Japanese Patent Application Publication No. 6-280934 entitled "Dynamic Vibration Damping Apparatus For Pendulum-Type Structure". This apparatus is supported on a hanger above a roof of a carriage of a cable car (passenger car). The hanger downwardly extends from the cable to the passenger car. The vibration damping apparatus has a size which does not protrude from the passenger car in its width and length directions in the horizontal direction so that it does not intervene the nearby structures. However, this vibration damping apparatus employs a spring-and-mass type attenuator. Use of a spring makes adjustment of a natural period of a damping mass difficult. In addition, the damping mass cannot oscillate in a large stroke since its stroke is limited by the spring and a dashpot. Further, its maintenance is not easy.